Conventionally, a ratio between blood pressures measured in a lower extremity and an upper extremity (a ratio between blood pressures in lower extremity and upper extremity) and a pulse wave propagate velocity or pulse wave velocity (Pulse Wave Velocity: PWV) are generally used as indicators of vascular disease such as arteriosclerosis (see, for example, Japanese Patent Laid-Open No. 2000-316821). For example, ABI, a ratio between systolic blood pressures measured in brachium and ankle, and TBI, a ratio between blood pressures measured in brachium and toe, are known as examples of a ratio between blood pressures in lower extremity and upper extremity, and ABI and TBI are used as indicators to show the presence or absence of arterial stenosis in lower extremity. On the other hand, a PWV is a propagation velocity of a wave generated with a movement of a vessel wall pressure in the aorta, the pressure being provided to a vessel wall when a heart feeds blood to the aorta. The faster velocity indicates a harder blood vessel. A PWV is calculated by measuring the same pulse wave at two different points on a blood vessel and a propagation time of the pulse wave, and dividing the distance between the two points by the propagation time.
However, since the pulse wave propagation velocity is affected by a blood pressure, correction is practically required depending on the blood pressure value. Moreover, because the relation between the blood pressure value and the amount of correction depends on the site in a body, the relation with respect to individual site should be examined beforehand, which virtually limits the sites to measure a pulse wave propagation time.
To solve the above problem, the applicant of the present invention has proposed the following formula as another indicator (see Japanese Patent Laid-Open No. 2005-152449):
Blood vessel elasticity index=1/k2(ln(Ps/Pd))•PWV2 
(where, k2 is a constant, Ps is a systolic blood pressure, and Pd is a diastolic blood pressure)
The blood vessel elasticity index (sometimes referred to as a degree of a vascular sclerosis) is useful as an indicator presenting the state of blood vessel at the time of measurement. On the other hand, because the vascular disease such as arteriosclerosis is so-called adult disease, regular measurements and observation of changes over time in the measured results is also important.
FIG. 9 is a conventional format to show changes over time in blood vessel elasticity indexes. This format presents the values, which were measured before on a common patient, in a two dimensional graph with a horizontal axis representing date, and a vertical axis presenting blood vessel elasticity index. The blood vessel elasticity indexes on left side body and right side body are presented in a separate sequence respectively.
In FIG. 9, the presentation of a plurality of measured values over time allows the changes over time in each blood vessel elasticity index to be understood by glancing at it, and a tendency toward deterioration or amelioration of symptoms to be checked.
However, there are useful other information such as ABI and blood pressure, in addition to the blood vessel elasticity index, in bioinformation related to vascular disease. It can be thought that a diagnosis from various perspectives can be made if changes over time in such information are also taken into account together with the changes over time in blood vessel elasticity indexes. However, because conventionally only the changes over time in blood vessel elasticity indexes have been presented, such report was used only for a diagnosis from the perspective of blood vessel elasticity index.